1. Field of the Invention
The present invention relates generally to a magnetic or linear scale which has a magnetic reading head providing signals corresponding to indicia recorded on a magnetic scale member to indicate accurately any relative displacement between the magnetic head and the magnetic scale member. More specifically, the invention relates to an improved magnetic reading head assembly which allows more precise and accurate indication of relative displacement of the magnetic reading head and the magnetic scale member, in comparison to the prior art. Even more specifically, the invention relates to a magnetic reading head assembly adapted for the type of magnetic scale which has a magnetic reading head essentially coaxial with the magnetic scale member.
2. Description of the Prior Art
As is well known, a magnetic scale or linear scale comprises a magnetic scale member and one or more magnetic reading head members. The magnetic scale member extends through openings through the magnetic reading heads so that the magnetic scale member and the magnetic reading heads can be displaced linearly along the axis of the magnetic scale member.
In order to perform accurate linear measurement of the relative displacement between the magnetic scale member and the magnetic reading heads, it is desirable to establish engagement between the openings of the magnetic reading heads and the magnetic scale member with minimum play therebetween so as to ensure truly linear movement of the magnetic reading head relative to the magnetic scale member. However, it has been considered difficult or even impossible to completely eliminate play between the magnetic reading head and the magnetic scale due to tolerances necessary for production. Such play between the opening of the magnetic reading head and the magnetic scale member allows misalignment of the magnetic reading head relative to the magnetic scale member during relative movement of the magnetic scale member and the magnetic reading head. This results in unstable movement of the magnetic reading head relative to the magnetic scale member.
In other words, it has been difficult to hold the axis of the opening of the magnetic reading head parallel to and in a predetermined positional relationship with the axis of the magnetic scale member, due to misalignment of the magnetic reading head relative to the magnetic scale member.